Treasury must turn over Trump’s taxes to Congress, the Justice Dept. says.

The Treasury Department must turn over former President Donald J. Trump’s tax returns to congressional investigators, the Justice Department said in a legal opinion issued on Friday that potentially paves the way for their release after a yearslong fight.

The House Ways and Means Committee had requested Mr. Trump’s tax returns for the years immediately before he became president as part of its review of the Internal Revenue Service’s presidential audit program. The Trump administration stymied the request and the committee sued to obtain the documents.

That review is a valid reason for the request, the Justice Department’s Office of Legal Counsel said in an opinion. “The chairman of the House Ways and Means Committee has invoked sufficient reasons for requesting the former president’s tax information,” the opinion said. “Treasury must furnish the information to the committee.”

The determination by the Justice Department comes more than a year after the Supreme Court ruled that Mr. Trump’s tax returns must be shared with the Manhattan district attorney’s office, which had sought them as part of a criminal investigation into the Trump Organization.

The Treasury Department intends to provide the documents to Congress as part of ongoing litigation, according to an administration official.

But the development does not necessarily mean that Mr. Trump’s tax information would immediately become public. Rules governing the sharing of sensitive tax information with the Ways and Means Committee require the panel to hold formal votes if it wants to share any of the information with the broader House or the public, or even include it in a committee report released to the public.

“As I have maintained for years, the committee’s case is very strong and the law is on our side,” Representative Richard E. Neal, Democrat of Massachusetts and chair of the Ways and Means Committee, said in a statement. “I am glad that the Department of Justice agrees and that we can move forward.”

Speaker Nancy Pelosi called access to Mr. Trump’s tax returns “a matter of national security” and said that “the American people deserve to know the facts of his troubling conflicts of interest and undermining of our security and democracy as president.”

Later on Friday, the committee and the Justice Department will inform the court that the executive branch intends to furnish the documents to Congress, according to multiple administration officials.

The court will then set a briefing schedule that will determine the next steps.